Vaso-occlusion devices are surgical implements or implants that are placed within the vasculature of the human body, typically via a catheter, to block the flow of blood through a vessel or an aneurysm stemming from the vessel via the formation of an embolus. One widely used vaso-occlusive device is a helical wire coil having windings that may be dimensioned to engage the walls of an aneurysm. Virtually all such vaso-occlusive implants are delivered by pushing the devices through wire-guided catheters.
As an example of an early vaso-occlusive device, U.S. Pat. No. 4,994,069, to Ritchart et al., describes a vaso-occlusive coil that assumes a linear helical configuration when stretched and a folded, convoluted configuration when relaxed. The coil assumes the stretched condition during delivery of the coil at the desired site by passage through the catheter, and assumes the relaxed configuration, which is better suited to occlude the aneurysm, once the device is so placed. Ritchart et al. describes a variety of secondary shapes, including “flower” shapes and double vortices. A random secondary shape is also described. Vaso-occlusive coils having little or no inherent secondary shape have also been described. For instance, in U.S. Pat. No. 5,690,666, to Berenstein et al., is found a coil having little or no shape after introduction into the vascular space.
Vaso-occlusive coils having materials added externally to the coil to enhance its therapeutic effect have also been manufactured. For example, vaso-occlusive coils having attached fibrous elements in a variety of secondary shapes are shown in U.S. Pat. No. 5,304,194. A vaso-occlusive coil with a fibrous woven or braided covering of a filamentary material is described in U.S. Pat. No. 5,382,259. And vaso-occlusive coils having a polymeric fiber wrapped around the wire of the primary coil or a polymeric covering wrapped around the primary shape of the coil are shown in U.S. Pat. No. 6,280,457.
There are a variety of ways of discharging shaped coils and linear coils into the human vasculature. In addition to those patents that apparently describe only the physical pushing of a coil out into the vasculature (e.g., Ritchart et al.), there are a number of other ways to release the coil at a specifically chosen time and site. U.S. Pat. No. 5,354,295 and its parent, U.S. Pat. No. 5,122,136, both to Guglielmi et al., describe an electrolytically detachable embolic device. In addition, a vaso-occlusive device with multiple detaching points was described in U.S. Pat. No. 5,941,888 to Wallace et al. A variety of mechanically detachable devices are also known, examples of which are disclosed in U.S. Pat. No. 5,234,437, to Sepetka, U.S. Pat. No. 5,250,071, to Palermo, U.S. Pat. No. 5,261,916, to Engelson, U.S. Pat. No. 5,304,195, to Twyford et al., U.S. Pat. No. 5,312,415, to Palermo, and U.S. Pat. No. 5,350,397, to Palermo et al.
Vaso-occlusive coils containing a means for preventing the stretching of the coil during movement of that coil are also known. For instance, in U.S. Pat. No. 5,833,705, to Ken et al., an implantable vaso-occlusive device is described in which a stretch-resisting member extends through the lumen of the outer helical coil and is attached to the coil at two locations. The stretch-resisting members can be made from polymeric filaments or other flexible materials. In U.S. Pat. No. 6,193,728, to Ken et al., a stretch-resistant vaso-occlusive coil is described in which the stretch-resisting member is indirectly attached to the coil via an anchor coil coaxially situated between the outer coil and the core wire. During manufacture of the coil assembly, which preferably involves the application of heat, care must be taken to avoid melting the polymeric filaments of the stretch-resisting member.
In another variation of the vaso-occlusive coil, instead of the anchor coil, a single twisted link, which has a loop at the distal end to connect with the stretch-resisting member, is utilized as the anchoring device in an attempt to distance the polymeric filament from the heated proximal end. Although this embodiment is successful in preventing the filament from melting, the single twisted link creates a stiff section at the proximal end of the coil. This stiff section can cause problems during placement of the coil in the aneurysm by preventing the proximal end from curving into the interior of the aneurysm. Rather, the stiff proximal end could extend through the mouth of the aneurysm into the parent artery where vaso-occlusion is not desired. In addition, the twisted anchor, with its relatively large diameter, is difficult to insert into vaso-occlusive coils with smaller lumens.
Accordingly, improved vaso-occlusive devices utilizing more flexible anchoring assemblies for the stretch-resisting member are desired.